U.S. patent application number 12/741212 was filed with the patent office on 2010-11-04 for protection of hygroscopic scintillators.
This patent application is currently assigned to Koninklijke Philips Electronics N.V.. Invention is credited to Cornelis R. Ronda, Herbert Schreinemacher, Guenter Zeitler.
Application Number | 20100276600 12/741212 |
Document ID | / |
Family ID | 40626277 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100276600 |
Kind Code |
A1 |
Ronda; Cornelis R. ; et
al. |
November 4, 2010 |
PROTECTION OF HYGROSCOPIC SCINTILLATORS
Abstract
A radiation detector (100) includes an array of scintillator
pixels (102) in optical communication with a photosensor. The
scintillator pixels (102) include a hygroscopic scintillator (104)
and one or more hermetic covers (106a, 106b). A desiccant (124) may
be disposed between a hermetic cover (106a) and the scintillator
(104) or between the hermetic covers (106a, 106b).
Inventors: |
Ronda; Cornelis R.; (Aachen,
DE) ; Zeitler; Guenter; (Aachen, DE) ;
Schreinemacher; Herbert; (Baesweiler, DE) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P. O. Box 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
Koninklijke Philips Electronics
N.V.
Eindhoven
NL
|
Family ID: |
40626277 |
Appl. No.: |
12/741212 |
Filed: |
October 29, 2008 |
PCT Filed: |
October 29, 2008 |
PCT NO: |
PCT/IB2008/054492 |
371 Date: |
May 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60986785 |
Nov 9, 2007 |
|
|
|
Current U.S.
Class: |
250/362 ;
250/367; 250/484.2; 427/123 |
Current CPC
Class: |
G01T 1/2018 20130101;
G01T 1/202 20130101; G01T 1/2002 20130101 |
Class at
Publication: |
250/362 ;
250/367; 250/484.2; 427/123 |
International
Class: |
G01T 1/20 20060101
G01T001/20; B05D 5/12 20060101 B05D005/12 |
Claims
1. An apparatus comprising: a first scintillator; a cover disposed
on a surface of the first scintillator and that hermetically seals
the scintillator, wherein the cover includes a metal layer.
2. The apparatus of claim 1 wherein the cover includes a wrapper
that covers at least a portion of the first scintillator, wherein
the metal layer forms at least a part of the wrapper.
3. The apparatus of claim 2 wherein the wrapper includes a
flexible, metalized polymer.
4. The apparatus of claim 1 including a desiccant disposed inside
the cover.
5. The apparatus of claim 1 wherein the cover includes a first
cover, a second cover disposed between the first cover and the
first scintillator, and a desiccant disposed between the first and
second covers.
6. The apparatus of claim 1 wherein the metal layer is formed on
the surface of the scintillator by way of evaporation or
precipitation.
7. The apparatus of claim 1 wherein the metal layer includes a
passivation layer formed on a surface of the scintillator.
8. The apparatus of claim 1 wherein scintillator includes a rare
earth metal and the metal layer includes one of a rare earth
oxycarbonate, a rare earth salt, or a rare earth tartrate.
9. (canceled)
10. (canceled)
11. The apparatus of claim 1 including a light transmissive window,
wherein the first scintillator, the cover, and the light sensitive
window form a first scintillator pixel for use in a radiation
detector that includes a second scintillator pixel and a
photosensor, wherein the first scintillator pixel includes a first
side that faces the second scintillator pixel and a second side
that faces the photosensor, wherein the metal layer covers at least
a portion of the first side and the light transmissive window
covers at least a portion of the second side; whereby, when the
first and second scintillator pixels are installed in the radiation
detector, scintillation photons produced by the scintillator pass
through the light transmissive window for detection by the
photosensor and are prevented from reaching the second scintillator
pixel by the metal layer.
12. The apparatus of claim 1 including a plurality of
scintillators, a plurality of covers, and a photosensor in optical
communication with a scintillator, wherein each cover is disposed
on and hermetically seals a corresponding one of the plurality of
the scintillators.
13. The apparatus of claim 1 wherein the scintillator and the cover
form a part of an imaging apparatus.
14. In a radiation detector including first and second scintillator
pixels in optical communication with a photosensor, a method
comprising: using a first cover including a first metal layer to
hermetically seal the first scintillator pixel; and using a second
cover including a second metal layer to hermetically seal the
second scintillator pixel.
15. The method of claim 14 wherein the first metal layer is
disposed on a first polymer substrate that covers at least a
portion of the first scintillator pixel and the second metal layer
is disposed on a second polymer substrate that covers at least a
portion of the second scintillator pixel.
16. (canceled)
17. (canceled)
18. The method of claim 14 wherein the first scintillator pixel
includes a scintillator material and the first metal layer is
formed on a surface of the scintillator material by evaporation,
precipitation, or passivation.
19. The method of claim 14 including using the first metal layer to
reflect scintillation photons produced by the first scintillator
pixel.
20. (canceled)
21. The method of claim 14 wherein the detector includes a third
scintillator pixel and the method includes using the first cover to
hermetically seal the third scintillator pixel.
22. A method comprising: applying a first optically opaque hermetic
cover to a first hygroscopic scintillator to form a first
scintillator assembly; applying a second optically opaque hermetic
cover to a second hygroscopic scintillator to form a second
scintillator assembly.
23. The method of claim 22 where the first cover includes a wrapper
and the method includes adhering the wrapper to the first
scintillator.
24. The method of claim 23 wherein the first scintillator is a
rectangular prism including six sides and the wrapper covers the
six sides.
25. The method of claim 22 wherein the scintillator includes a rare
earth and the first cover includes a rare earth oxycarbonate or a
rare earth tartrate.
26. The method of claim 22 wherein applying the first cover
includes precipitating a metal carbonyl.
27. The method of claim 22 including assembling the first
scintillator assembly, the second scintillator assembly, and a
photosensor in a radiation detector.
28. (canceled)
29. A radiation detector comprising: a pixellated scintillator; a
cover disposed on and that hermetically seals at least a first
pixel of the pixellated scintillator, wherein the cover includes a
metal layer; a photosensor in optical communication with the first
pixel.
Description
[0001] The present application relates to the protection of
moisture sensitive scintillators.
[0002] Various applications in fields such as high energy physics,
medical imaging, non-destructive testing and other industrial
applications, threat detection, oil well logging and other
geological exploration applications rely on the ability to detect
radiation such as energetic photons (e.g., x-rays and gamma rays)
and particle radiation (e.g., neutrons). Systems in these and other
fields have employed radiation detectors to detect the radiation of
interest, with suitable signal processing circuitry being used to
process the detector signals to suit the requirements of the
application.
[0003] In medical imaging applications such as positron emission
tomography (PET) and single photon emission tomography (SPECT), for
example, signals from a number of such detectors are processed to
produce images indicative of the distribution of a
radiopharmaceutical in a patient. These images can play a
significant role in the diagnosis and treatment of diseases such as
cancer and heart disease.
[0004] The detectors in these and other systems have employed a
scintillator that produces scintillation photons in response to
received radiation. A photosensor in optical communication with the
scintillator receives the scintillation photons and produces a
corresponding output signal for processing.
[0005] The scintillator can play an important role in the
performance of the detector and hence the overall performance of
the system. Although the precise requirements are generally
application-specific, the ideal scintillator would in general have
a high stopping power, produce a high light output, possess fast
response and decay times, and be mechanically and environmentally
robust.
[0006] One class of scintillators that has garnered significant
attention is that of rare-earth halide scintillators of the general
formula LnX.sub.3, where Ln represents a rare earth ion and X is
selected from the group of chlorine (Cl), bromine (Br), and iodine
(I). Unfortunately, however, these materials are sensitive to
moisture, exposure to which can negatively affect scintillator
performance.
[0007] Because the production and/or structuring the scintillator
can generally be performed in an inert atmosphere, the hygroscopic
nature of these materials is ordinarily not a significant drawback
during the manufacturing process. In transport and use, however,
the scintillators and the systems in which they are used must often
be placed in moisture-laden environments. Unless suitably
protected, performance of the scintillator and hence the system in
which it is used may be sub-optimal.
[0008] Aspects of the present application address these matters and
others.
[0009] In accordance with one aspect, an apparatus includes a
scintillator and a cover. The cover is disposed on a surface of the
scintillator and hermetically seals the scintillator. The cover
includes a metal layer.
[0010] In accordance with another aspect, in a radiation detector
including first and second scintillator pixels in optical
communication with a photosensor, a method includes using a first
cover including a first metal layer to hermetically seal the first
scintillator pixel and using a second cover including second metal
layer to hermetically seal the second scintillator pixel.
[0011] In accordance with another aspect, a method includes
applying a first optically opaque hermetic cover to a first
hygroscopic scintillator to form a first scintillator assembly and
applying a second optically opaque hermetic cover to form a second
scintillator assembly.
[0012] According to another aspect, a radiation detector includes a
pixellated scintillator, a cover disposed on and that hermetically
seals at least a first pixel of the pixellated scintillator,
wherein the cover includes a metal layer, and a photosensor in
optical communication with the first pixel.
[0013] Still further aspects of the present invention will be
appreciated to those of ordinary skill in the art upon reading and
understand the following detailed description.
[0014] The invention may take form in various components and
arrangements of components, and in various steps and arrangements
of steps. The drawings are only for purposes of illustrating the
preferred embodiments and are not to be construed as limiting the
invention. Those of ordinary skill in the art that, for ease of
illustration, the present drawings are not necessarily to
scale.
[0015] FIG. 1 is a top view of a radiation detector.
[0016] FIGS. 2A, 2B, and 2C depict cross sectional views along the
line 2-2 of FIG. 1.
[0017] FIG. 3 depicts a radiation detection apparatus.
[0018] FIG. 4 depicts a method.
[0019] FIG. 5 depicts a method.
[0020] With reference to FIG. 1, a radiation sensitive detector 100
includes a plurality of scintillator pixels 102 arranged in a
two-dimensional array. The various scintillator pixels 102 include
a scintillator 104 and a cover 106 that is disposed on a surface of
and hermetically seals the scintillator 104.
[0021] The scintillator 104 includes a hygroscopic or moisture
sensitive scintillator material such as a (suitably doped) rare
earth halide having the general formula LnX.sub.3, where Ln
represents a rare earth ion and X is selected from the group of
chlorine (Cl), bromine (Br), and iodine (I). Other hygroscopic
scintillator materials are also contemplated, however, and may be
selected based on application-specific requirements. The various
scintillators 104 take the form of a six (6) sided rectangular
prism each having a volume on the order of about 0.5 to 1.0 cubic
centimeters (cm.sup.3), although other shapes and sizes are
contemplated.
[0022] Though illustrated as a two dimensional, regular array, the
various scintillator pixels 102 may be configured an irregular
array, (e.g., with scintillators 104 having different sizes or with
adjacent rows and/or columns offset by a fraction of the pixel 102
pitch), as a one-dimensional array, including only a single
scintillator pixel 102, or the like.
[0023] FIG. 2A depicts a first cross-sectional view of the detector
100. As illustrated, the detector 100 includes a photosensor 108
such as one or more photomultiplier tubes (PMTs), photodiodes,
silicon photomultipliers (SiPMs), charge coupled devices (CCDs),
complementary metal oxide semiconductor (CMOS) photosensors, or the
like in optical communication with the various scintillator pixels
102. A layer of light transmissive adhesive 114 such as an optical
epoxy couples the bottom or light emitting faces 110 of the
scintillator pixels 102 and the top or light receiving face 112 of
the photosensor 108.
[0024] Thus, gamma or other radiation 116 received at the top or
radiation receiving face 118 of the detector 100 interacts with the
scintillator 104 to produce scintillation photons 120 that are
received by the photosensor 108. Where the side or top face(s) of
the scintillator pixels 102 are optically reflective, scintillation
photons 120 may be reflected at the respective face(s). Where, on
the other hand, the face or faces are optically absorbent, photons
120 may be absorbed at the respective face(s).
[0025] In the illustrated embodiment, the hermetic cover 106
includes a metal layer that hermetically seals the various
scintillator pixels 102 on five (5) of their six (6) faces. A light
transmissive window 122 formed from a relatively
moisture-impervious material such as a polymer, a light
transmissive adhesive, glass, quartz, or the like protects the
light emitting face 110. A particular advantage of the illustrated
arrangement is that the scintillator pixel 102 is substantially
sealed, thereby tending to reduce the environmental constraints
imposed on the remainder of the manufacturing process.
Alternatively, the window 122 may be omitted, in which case
hermetic sealing of the light emitting face 110 is performed by the
light transmissive adhesive 114.
[0026] In one embodiment, the cover 106 includes a moisture
impervious wrapper that is wrapped around each of the various
scintillators 104 on substantially five (5) sides. The wrapper may
include a flexible polymer substrate having a thin metal layer
deposited thereon. One suitable material for the wrapper is a thin
polyester film coated on one or both sides with a layer of
aluminum, which material is sometimes referred to as aluminized
Mylar.TM.. The wrapper may also be formed from a thin metal foil. A
layer of adhesive adheres the wrapper to the surface of the
scintillator 104, particularly in the vicinity of those edges that
may be exposed to moisture.
[0027] The wrapper may also extend to cover the sixth face 110 of
the scintillator 104. Note that, in order to provide for light
transmission between the scintillator 104 and the photosensor 108,
the metal layer should be omitted from that portion of the
substrate that covers the light transmissive face 110. Again, such
an arrangement tends to reduce the environmental constraints
imposed on the manufacturing process.
[0028] In another embodiment, the cover 106 includes a thin metal
layer that is applied to the surface(s) of the scintillator 104 by
evaporation or precipitation, with the metal layer again being
omitted from the light emitting face 110. Application of the metal
layer via evaporation is particularly attractive in the case of
metals such as aluminum or zinc that can be evaporated relatively
easily. Application by way of precipitation may be performed using
metals such as tungsten or nickel that can be obtained in the form
of metal carbonyls (e.g., W(CO).sub.6 or Ni(CO).sub.4). These
molecules precipitate on the scintillator surface and decompose,
leaving behind a thin metal layer. The process can be accelerated
by exposing the scintillator to an elevated temperature, for
example in the vicinity of about 400 Kelvin (K).
[0029] In another embodiment, the cover 106 includes a chemical
passivation layer. Such an implementation leverages the fact that
rare earth halides react at elevated temperature with a mixture of
water vapor and carbon dioxide to form chemically inert rare earth
oxycarbonates (e.g., of the form (LnO).sub.2CO.sub.3 where Ln is
the rare earth metal). The resultant chemical passivation layer may
be used to hermetically seal the desired surface(s) of the
scintillator.
[0030] In a yet even other embodiment, the rare earth halides are
treated carefully with bidentate organic acids such as tartartic
acid, e.g. dissolved in water. The rare earth halides react with
this solution, to form water insoluble rare earth tartrates. The
same procedure may be used with other acids, forming other water
insoluble rare earth salts, like boric acid.
[0031] As the above materials are ordinarily optically opaque, such
an arrangement also tends to reduce undesirable optical cross-talk
between the various pixels 102 when installed in an array. Where
the metal layer is optically reflective, the metal layer may also
tend to improve the detector optical efficiency.
[0032] Note that a scattering layer formed from a material such as
a titanium dioxide (TiO.sub.2) may also be applied to the various
faces of the scintillator 104 prior to application of the covering
106. Again, the scattering layer would ordinarily be omitted from
the light emitting face 110.
[0033] Notwithstanding the hermetic sealing provided by the covers
106, it is possible that moisture may, over time, diffuse through
or otherwise find its way inside the covers 106. Thus, and as
illustrated in FIG. 2B, a desiccant 124 may be placed between the
cover 106 and the scintillator 104 as an aid to maintaining a state
of dryness within the cover 106. Such an arrangement is
particularly beneficial in which the cover 106 is formed using a
wrapper as described above. Suitable desiccants 124 include calcium
oxide (CaO), phosphorus pentoxide (P.sub.2O.sub.5), calcium
chloride (CaCl.sub.2), and molecular sieves formed from materials
such as zeolites.
[0034] Another alternative is presented in FIG. 2C. As illustrated,
the cover 106 includes a first, inner cover 106a and a second,
outer cover 106b, with the desiccant 124 located therebetween.
Again, such an arrangement is particularly suitable for
implementations in which the cover layers 106a, 106b are formed
from wrappers as described above. Alternately or additionally, the
desiccant 124 may be located between the inner layer 106a and the
scintillator 104.
[0035] Note also that the scintillators pixels 102 need not be
individually covered or wrapped. Thus, for example, a given cover
106 may be used to seal multiple scintillator pixels 102.
[0036] Turning now to FIG. 3, a radiation detection apparatus 300
employs one or more detectors 100.sub.1, 2, . . . n. As
illustrated, the detectors 100 are assembled to form a detector
assembly 302, which may likewise form a sub-assembly of a larger
system. In the case of a positron emission tomography (PET) system,
for example, one or more detector assemblies 302 are typically
arranged about an examination region in a generally circular or
other ring-shaped arrangement so that the radiations sensitive
faces face generally inwardly toward the examination region.
[0037] Data acquisition circuitry 304 such as one or more signal
conditioners, amplifiers, timers, analog to digital converters, and
the like condition and otherwise acquire the signals produced by
the detectors 100. As will be appreciated, the nature and function
of the data acquisition circuitry 304 is ordinarily apparatus 300
dependent. Again to the example of a PET system, the data
acquisition circuitry 304 may include coincidence detection, time
of flight measurement, energy measurement, and related
circuitry.
[0038] The data processor 306, the nature and function of which is
likewise apparatus dependent 300, further processes the acquired
data. Again to the example of a PET system, the data processor 306
may include a reconstructor that reconstructs the acquired data to
produce volume or image-space data indicative of the spatial
distribution or radionuclide decays in an object under
examination.
[0039] An interface 308 provides an interface between the data
processor 306 and a human user, a system or network, or the like.
Again to the example of a PET system, the interface 308 may present
the image space data in a human perceptible form or for storage in
a suitable computer readable storage medium.
[0040] Operation will now be described with reference to FIG.
4.
[0041] At 402, the cover(s) 106 are used to hermetically seal the
scintillators 104 of the various scintillator pixels 102. Thus, for
example, a first cover including a first metal layer hermetically
seals some or all of the surfaces of a first scintillator, and a
second cover including a second metal layer hermetically seals some
or all of the surfaces of a second scintillator.
[0042] At 404, the desiccant 124 may be used to maintain a state of
dryness inside the covers 106.
[0043] At 406, radiation 116 is received at the radiation receiving
face of the 118 of the detector 100.
[0044] At 408, the received radiation 116 interacts with a
scintillator 104, producing scintillation photons 120.
[0045] At 410, and depending on the optical characteristics of the
cover 106, scintillation photons 120 may be reflected and/or
absorbed by the metal layer.
[0046] At 412, the scintillation photons 120 are detected by the
photosensor 108, which generates corresponding output signals.
[0047] At 414, the output signals are acquired by the data
acquisition circuitry 304.
[0048] At 416, the acquired data is processed by the data processor
306.
[0049] At 418, an output indicative of the processed data is
presented via the interface 308.
[0050] Fabrication will now be described with reference to FIG.
5.
[0051] A suitable scintillator material is fabricated at 502 using
known techniques, for example by way of crystal growth or sintering
process. In one embodiment, the scintillator material includes a
rare earth halide.
[0052] At 504, the scintillator material is processed, for example
to form scintillators 104 for use in a pixelated scintillator
array. In one implementation, and as noted above, the scintillators
have a volume between about 0.5 and 1.0 cm.sup.3.
[0053] At 506, the hermetic cover 106 is applied to the
scintillators 104. Where the covering 106 includes a wrapper, for
example, the various scintillators 104 may be individually wrapped.
Alternatively, the cover 106 may be applied to various pixels via
an evaporative, precipitation, passivation or other suitable
technique. Again depending on the particular implementation, an
optical window 122 may also be applied.
[0054] At 508, the scintillator pixel(s) 102 and suitable
photosensor(s) 108 are assembled to form the radiation detector
100.
[0055] At 510, one or more radiation detectors 100 are assembled in
a detector assembly 302.
[0056] At 512, one or more detector assemblies 302 are assembled in
a radiation detector system 300.
[0057] The invention has been described with reference to the
preferred embodiments. Modifications and alterations may occur to
others upon reading and understanding the preceding detailed
description. It is intended that the invention be construed as
including all such modifications and alterations insofar as they
come within the scope of the appended claims or the equivalents
thereof.
* * * * *